The AM Forum

I have always used copper conductors for my antennas. But recently I wanted to try a V beam given the space I have available.  The models looked good.  Then, realizing that copper would be too soft I looked at steel alternatives, only I haven't found the resistivity of copper-weld yet. But thinking like a (cheap) ham, what about galvanized electric fence wire? I found the resistivity/Km for that  (15 and 26 ohm/km depending on gauge) and plugged it into the model along with a small >1 number for u.

Well!  There went that antenna pattern!  Quite an eye opener, to say the least.  More modeling is certainly in order.

So has anybody else compared clad steel wires with copper; or know the r and u specs for copper clad steel?

Mark

I like #10 or #8 solid copper. It will stay up for a long time if you have enough sag to handle tree movement. Pull it up tight and it will fall down in 6 months.

Considering the skin effect, copper clad steel will have about the same conductivty as solid copper at RF.

I wonder if the specs for the Cu clad reflect that. I haven't found any numbers yet.  And the model certainly makes some use of the u of the wire, but I would think that would tend to increase the skin effect without detriment.

Hmmm.
Just looked up the specs for "copper-weld" and they look somewhat better than galvanized steel fence wire. # 12 was 13 and 17 ohms/Km, that's about 1/3 of the fence wire. But still WAY short of copper.

Receive only?
Transmit/receive service?

For receive it makes zip difference for sure. :D

Not sure it makes any real world difference on 75m transmit either.

The copper clad fence stuff is thin.
I have used galvanized steel #14 for long wire receive ants.
Very strong stuff, nil stretch.
They make it in #16 and #18 I think... Agway, etc...

Copper stretches in long unsupported lengths will of course sag and stretch.
Thin copper in long stretches may break. Maybe not, some folks have had magnet wire dipoles up for quite some time...

Mark, throw up whatcha got and try it, then you can perfect it, if it is needed.
Won't work worth a darn if you use perfect materials the first time any how!  ;)

                        _-_-bear

If they acquired those numbers by testing with DC or even 60 Hz AC, then those numbers aren't really relevant. DC will see more of the steel core than RF will.

Timtron can give you some good first-hand testimonial on the use of copper-clad steel. His shaded dipole and wire array are both copper-clad from stem to stern, and he's had plenty of experience making identical antennae out of both straight copper and copper-clad.

Bear,
xmit and recv.

The resistivity of the wire makes a BIG difference in pattern according to the modeling.  Any directivity is completely lost.  More research is definitely in order.  I've had good luck with copper up to 125'. Breakage is inevitable over time but this application will be over 360' per leg which gets awfully heavy and tight for copper alone without significant sag.

clad is fine until the clad rots off.
360 feet is a long run. Any chance fora support in the middle like insulators hanging off a rope across the middle.

.

I use copper-clad steel #14 stranded for my antenna, it has not rusted at all.   But, my window line is made with the same type of wire for its conductors and where it has been exposed, it has almost completely rusted away.   I redid the connections and sprayed the exposed wire with autobody undercoating.    Some wire must have more copper cladding than others.

Mark,

I am surprised to say the least that a change in the resistivity of wire will effect the antenna pattern in a meaningful way!!

Makes not much sense.

I could see it perhaps if some significant resistance was there - like carbon (resistor) wire was in there, but not with "regular wire"... and if this is true, then the question becomes why this should occur??

Perhaps there is a bug in the antenna software? Seems more likely. But I am hardly an RF expert.
Can anyone shed light on this??

                      _-_-bear

Bear,
It makes sense to me. Without turning this into an antenna theory session, suffice to say that the "real" component of any antenna is exceedingly low, ideally zero. It doesn't take much actual resistance, "real" real so to speak, to trash the antenna's efficiency. In this case, the infinite series of isotropic sources whose vectors sum to form the antenna's pattern are equally trashed. Hence the pattern is no longer produced.
I knew this to be the case for efficiency on small mobile antennas but never really thought of the effect on the pattern of very long antennas whose "radiation resistance" (a very misunderstood term) is much higher. 

BTW, for the group, I've found very little of substance regarding the impedance of copper clad steel (CCS) at RF frequencies.  I found plenty of folks, and advertisers, who state what Steve said regarding skin effect, but only one fellow actually put a piece on an impedance bridge. His results lacked detail as his investigation was not focused on CCS, but his findings were significantly in favor of solid copper by a factor of 3.  I'm still looking for more data.  We hams have been using CCS for antennas so long you'd think this would be a moot question, but so far finding little or know serious metrics on the matter, maybe it's less than moot. 

We'll keep digging.  Of course, SOME OF US, are lucky enough to have some phosphor-bronze wire where strength and conductivity are equally abundant, but that wouldn't be me.

RF goes about .0008 inches deep at 1 MHz. Everything is fine until the plating degrades.

I find .0008" amazing.  To think how much conductor goes unutilized...
It looks like I'm going to need some light weight, 14AWG or less, GOOD copper-weld.  I've seen lots of the cheap stuff that has such a light wash of copper there's a little iron oxide on the spooled NOS wire already.

And Frank (I think you asked) there's really no way to support these wires mid-span. They sort of span a depression with little or no trees around them.   If you BING map my QTH they'll go from the pond and extend SSW and WSW from their.  The pond is some 50' lower than the wire's southern terminus. There just happens to be a few big trees on the ponds north side.

What is the operating frequency and angle between the legs? Height? Terminated or unterminated?

360 feet is about 1.5 WL at 3.9 MHz. Unless you can get that thing up over 100 feet, I don't see much gain.

The RF resistance of #12 copper wire is about 10 Ohms per wavelength at 1 MHz. It's about 2.5 Ohms per wavelength at 4 MHz.  Surface area is what you want.

Steve,
height will vary, but on average 50 feet is a fair approximation.   360 feet is the distance I have to work in but 310 is what I modeled for a reasonable dip on 3.9MHz.  Included angle is 60 degrees but may end up being wider. The gain I saw was 6.85db @ 35 degrees.   If I had the supports I'd rather do a driven array but...

I modeled 75 degrees on a guess. The TO angle is lowered. I'm seeing about 3 dB over a dipole at the same height at 36 degrees elevation. Not bad for only 50-60 feet in height.

I knew I had this chart somewhere. No CopperWeld though.  >:(


------------------------------------------ Ohm / Lambda--------------------
B&S dia | Dc.     1.825    3.5    7.0   10.1   14.2   18.1   21.2   29.0
AWG mm  | mOhm/m    MHz    MHz    MHz    MHz    MHz    MHz    MHz    MHz
---------------------------------------------------------------------------
36 0.13 | 1356.4 329.59 195.37 114.92  89.43  71.08  60.62  54.77  44.84
34 0.16 | 841.0  223.82 135.88  82.17  64.82  52.16  44.84  40.72  33.64
32 0.20 | 536.5  158.03  98.24  60.95  48.64  39.54  34.21  31.19  25.94
30 0.25 | 337.1  112.16  71.47  45.44  36.65  30.05  26.14  23.90  19.99
28 0.32 | 212.2   81.15  52.94  34.38  27.97  23.09  20.17  18.48  15.52
26 0.40 | 133.5   59.67  39.76  26.28  21.52  17.85  15.64  14.36  12.10
24 0.51 |  83.9   44.56  30.23  20.26  16.67  13.89  12.20  11.21   9.47
22 0.64 |  52.8   33.72  23.20  15.71  12.98  10.84   9.54   8.78   7.43
20 0.81 |  33.2   25.82  17.96  12.26  10.16   8.51   7.50   6.91   5.85
18 1.02 |  20.9   19.89  13.96   9.59   7.96   6.68   5.89   5.43   4.61
16 1.29 |  13.1   15.44  10.90   7.52   6.26   5.26   4.64   4.28   3.64
14 1.63 |   8.3   12.04   8.54   5.92   4.93   4.15   3.66   3.38   2.87
12 2.05 |   5.2    9.42   6.71   4.66   3.89   3.27   2.89   2.67   2.27
10 2.59 |   3.3    7.40   5.28   3.68   3.07   2.59   2.29   2.11   1.80
 5 4.62 |   1.0    4.07   2.92   2.04   1.71   1.44   1.27   1.18   1.00
 1 7.35 |   0.4    2.54   1.83   1.28   1.07   0.90   0.80   0.74   0.63
 2 5.40 |   0.0    0.73   0.53   0.37   0.31   0.26   0.23   0.21   0.18
 100.00 |   0.0    0.18   0.13   0.09   0.08   0.07   0.06   0.05   0.05
 500.00 |   0.0    0.04   0.03   0.02   0.02   0.01   0.01   0.01   0.01
--------------------------------------------------------------------------

The military made a stranded copper wire (about 14 gauge equivalent) with a kevlar rope center. If you could find some of this, you would be set.

 -- Just looked and Wireman makes something similar. See items 512 and 512A.

http://www.thewireman.com/antennap.html

present 160 meter antenna is a Vee 125 feet on a leg facing west. They work if the angle isn't too tight.  I use #8 solid fed with #10 solid spaced 4 inches.
360 feet with #8 would be very heavy. Kevlar would be very cool.